1. Field of the Invention
The invention concerns bulk material sorting methods and apparatus, and in the sorting of materials such as particulate recycled glass from municipal recycling materials.
2. Prior Art
Municipalities routinely collect glass for recycling; however even after substantial washing and sorting steps, the composition of the collected glass is not uniform. Processors attempting to use the recycled glass find, for example, that some of the glass particles melt at a higher temperature than others, which leads to processing problems that render the recycled material unsuitable for certain uses. Recycled glass materials comprise containers and broken glass pieces that are clear (or xe2x80x9cflintxe2x80x9d) or colored, typically amber or green. When collected for recycling, various non-glass contaminant materials are present. Non-glass contaminants having physical properties that are distinctly different than those of the glass can be sorted out by discriminating for differences in properties. For example, metal bottle caps and the like can be removed during crushing and screening steps because metal is malleable and is flattened by crushing, but glass is frangible and breaks into small pieces that can be screened. Ferromagnetic metals can be removed magnetically. Contaminants such as organics, dirt, paper from labels and the like can be removed by washing, rinsing and filtering steps. Plastics are generally less dense than glass and can be removed by rinsing, skimming or winnowing steps.
A greater problem is confronted in attempting to sort out materials that have properties that are quite similar to those of glass. Occasional pieces of ceramics, pyroceramics (e.g., Corning Corelle ware), tempered glass (e.g., Corning Pyrex glass), stones and other materials are frequently present in the recycled cullet. These contaminants are not readily distinguishable from glass by their physical properties, which in many respects resemble the properties of glass. Most sorting techniques are not effective to detect and remove them because their physical, electrical and chemical properties are substantially the same as those of glass. Recycling authorities accordingly may instruct consumers to recycle only glass food and beverage containers, and not (for example) glassware, crystal, ceramics, plate glass, mirrors and the like. Inevitably some of these materials find their way into recycled glass.
Contaminants can cause difficulties in processing cutlet into new glass. The recycling process typically includes comminuting the glass into relatively small particles that are processed in bulk. Particles that have properties that are distinct from those of the other particles represent defects in the bulk material. For example, ceramics and tempered glass have a higher melting temperature than glass, such that they may not melt completely and/or mix homogeneously in remelted glass. The result may be localized defects in molded recycled glass, clogging of spinnarettes used to make fiberglass from recycled glass, and other problems. For these reasons, recycled glass may be relegated to uses taking negligible advantage of its properties, such use as a filler in paving material. On the other hand, it is impractical or impossible to manually pre-sort cutlet effectively before comminution or breakage.
Many types of materials are recycled, such as glass, plastic, paper and metals, often in mandatory programs intended to reduce waste and conserve landfill space. A municipality may require that recycled materials be sorted manually into different containers that are dumped into different receptacles upon collection. More often, there are too many categories to justify segregation of each variety of material through the process. Typically glass, plastic and metal are collected together for later sorting. Even if an attempt is made to sort by material, consumers cannot be expected to be sensitive to a difference in types of glass, and may commingle distinct materials inadvertently.
Recyclables collected in commingled collection programs need to be sorted during further processing if a relatively pure material is needed, for example to make new glass containers or the like from the recycled ones. Manual sorting is possible but tends to be prohibitively expensive, and the most careful sorting can be ineffective when much of the glass is broken. Due to the inability to sort types of glass and to separate glass and non-glass materials, recycled glass cutlet often is not used to make new glass, and is substantially less valuable than material that is more pure. For example, recycled glass cullet of moderate particle size may be used as an aggregate or filler in roadway paving. Smaller particles may be used as xe2x80x9csandxe2x80x9d for golf course bunkers. Although these uses are not insubstantial, the economic and product purity issues are such that approximately 85% of recycled mixed cullet goes into landfills.
There can typically be up to 10% contaminants in recycled glass material, i.e., 200 lbs. per ton. It would be advantageous if recycled glass could be sorted more effectively to remove non-glass materials, ceramics, pyroceramics and tempered glass.
In addition to avoiding waste of material, glass cullet liquifies at a lower temperature than new glass batch, and has favorable viscosity characteristics. Less heat energy is necessary to melt cullet than new batch, reducing costs and environmental emissions. Processing time is reduced, improving productivity. It would be advantageous to use recycled glass to make new glass containers, fiberglass and other products in order to conserve resources and reduce costs.
For all these reasons, it would be advantageous to provide a more practical technique to distinguish and sort glass and non-glass materials having properties similar to glass, which can be operated on a production scale. The present invention provides a method and means for distinguishing and substantially removing various contaminant materials by taking advantage of their different mechanical, electromagnetic, and thermal characteristics.
The invention concerns bulk material sorting methods and apparatus, and in particular to sorting materials such as particulate recycled glass.
More particularly, the invention is an apparatus, system, and method for sorting a stream of mixed particulates of at least two distinct materials having different mechanical, chemical, electromagnetic, and thermal characteristics, especially different characteristics between particulate glass and contaminants such as pieces of polymer, metal and metallics, ceramics, pyroceramics, tempered glass, and stones and assorted silicates. The system of the invention comprises a series of sorting and refining stations that are adapted to separate the cullet into useable glass and non-glass debris, comprising of a cullet intake station, a metal sorting station, a screening station, a crushing station, vacuuming equipment, a wash station, a shaker-feeder station, a drying station, a metal detection and removal station, and a ceramic detection and removal station, a pulverizing station, a multi-deck screening station, and a loading and storage station. Typically, the unsorted particulate material is collected in a thick mass and moved, from station to station, by a series of conveyors.
First, a stream of mixed particulates is delivered from the intake station to the metal sorting station where a magnetic separator separates the mixed particulates into a magnetic fraction and a non-magnetic fraction. The non-magnetic fraction is further divided into a coarse component and a fine component at the screening station. The resulting coarse components are further crushed and admixed with the fine component at the crushing station. A series of vacuuming equipment operates to remove air-borne chaff from the non-magnetic fraction.
The resulting non-magnetic particulates continues through this system to the washing station. After the washing stage, the particulates are delivered to the shaker-feeder station where a vibrating conveyer and a vibrating perforated deck removes bulk moisture from the particulates. The washed particulates are further dried by going through the drying station. The substantially dried particulates then move through the metal detection and removal station where a separation of non-magnetic metal particulates from the non-magnetic fraction occurs. At this point of the process, all of the metallic particulates have been removed.
The resulting particulates then go through a ceramic detection and removal station where particulates having non-glass characteristics are separated from particulates having characteristics of glass. At this point, the resulting glass material is clean, dry and pure and can be used to make glass products.
After passing through the ceramic detection and removal station, the resulting glass material can be further refined and divided by a pulverizing station and a multi-deck screening station. As an alternative to the multi-deck screening station, a density separation station can be used to further refine the material. The final product is a clean, dry, and fine granular glass powder which can be used for making glass products. The resulting physical properties of the glass powder are such that the glass powder acts as a flux and melts at lower temperatures thus requiring less power for making glass compared to regular raw glass material. This product also has 0% fusion loss compared to 15% fusion loss for regular raw glass material.
Additional aspects and objects of the invention will be apparent in connection with the following discussion of practical examples.